diff --git a/rbinvariantslib/utils.py b/rbinvariantslib/utils.py
index d19d5ce..d9cfe91 100644
--- a/rbinvariantslib/utils.py
+++ b/rbinvariantslib/utils.py
@@ -3,7 +3,6 @@
 """
 from typing import Tuple
 
-from ai import cs
 from astropy import units
 import numpy as np
 import numpy.typing as npt